This invention relates to a blow-moldable rigid thermoplastic polyurethane resin and a method for preparing same.
There is a potentially large market for blow-molded grade rigid thermoplastic polyurethane resins (RTPUs), such as ISOPLAST.TM. engineering thermoplastic resins, if such resins could be obtained with sufficiently increased melt strength over current resins. Catalysts which are typically used to promote polymerization to form RTPUs also contribute to depolymerization at temperatures where blow-molding is ordinarily carried out. This depolymerization results in a reduction in melt strength, which is undesirable for blow-molded grade RTPUs.
Laughner, in U.S. Pat. No. 5,094,806 (incorporated herein by reference), describes a method of improving melt strength of a variety of thermoplastic polyurethane resins through addition of a small amount of a fluorinated olefinic polymer or copolymer and, optionally, an impact modifier. Unfortunately, these fluorinated polymers are expensive and somewhat difficult to handle.
It would be desirable, therefore, to provide a blow-moldable RTPU which is inexpensive and easy to scale up.